| 85Kr and 39Ar are both radio-noble gas isotopes,their chemical inertness make them ideal environmental tracers.85Kr has a half-life of 10.74 years and is mainly produced during reprocessing of spent nuclear fuels.This makes it an important tracer in environmental monitoring,atmosphere study and nuclear safety.It can also be used to date environmental water samples in the past 50 years,such as shallow groundwater,surface seawater and mountain glacier ice.39Ar has a half-life of 268 years.Its dating range is 50-1800 years,which bridges the dating gap between the transient tracers like 85Kr,3H and the long lived 14C.Its unique dating range makes it a valuable tracer in dating mountain glacier ice and tracing the circulation of ocean currents.The isotopic abundances of 85Kr and 39Ar are both very low(2×10-11 and 8 × 10-16),which make their detection extremely challenging.The traditional ultrasensitive trace analysis method,such as Low Level Counting(LLC)and Accelerator Mass Spectrometry(AMS),do not work well for these isotopes.As a result applications of 85Kr and 39Ar in earth science and environmental monitoring are hampered.The detection problem of 85Kr and 39Ar has been solved by the Atom Trap Trace Analysis method.Progress on applications of 85Kr and 39Ar dating has been made recently.The ATTA method is still evolving rapidly.Many key technical problems are yet to be studied and solved.This thesis is focused on the sample processing method and the ATTA method,which are key problems in radio-krypton and radio-argon dating.The main works of this thesis include:1)Development of sample processing method.In this part,a continuous air sampling and krypton purification method has been developed.An automatic air processing apparatus has been built and can work synchronously with the ATTA instrument.Based on this technology,online monitoring of atmospheric 85Kr activities has been demonstrated.This works features hourly time resolution and sample requirement of only 3 L of air.Both are improved by orders of magnitude compared to traditional 85Kr monitoring techniques.The technology reported in this thesis can be used in remote monitoring of fuel reprocessing plants.2)Development of the ATTA method.Systematic investigation on using the optical pumping method to improve the 39Ar atom count rate in ATTA has been conducted.Energy levels suitable for the optical pumping scheme have been selected based on theoretical calculations and experiments.The gain factors on the 39Ar atom count rate under different optical pumping conditions,as well as the hyperfine structure of related energy levels have been measured.In the optical pumping experiment,39 Ar atom count rate is improved by two times.These works would eventually improve the efficiency of the 39 Ar ATTA method,thus both improving the analytical precision and reducing the analysis time,which promotes the applications of 39Ar dating.The contents of this thesis are organized as follows:Chapter 1 is an introduction about radioactive krypton and radioactive argon dating and atomic trap trace analysis technique.In Chapter 2,the principles and the details about the automatic air sampling and Kr purification system along with an introduction about monitoring of atmospherics 85Kr activities are presented.In Chapter 3,we present the experimental work on online measurement of atmospheric 85kr activities.In Chapter 4,an introduction of the 39Ar ATTA method and its applications and the details about the construction of the ATTA apparatus for 39Ar are presented.The experimental methods used to characterize the apparatus are presented as well.In Chapter 5,we present the works on improving the 39Ar atom count rate by the optical pumping method,including theoretical calculations and experiments.In Chapter 6,a summary about the works presented in this thesis and some outlooks on radio-krypton and radio-argon dating base on the ATTA method are given. |
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